The structure, organization, expression, and evolution of the genes for the crystallins of the eye have been examined. A single AlphaA-crystallin gene has been found in the mouse. This gene produces both the AlphaA2 and AlphaAins polypeptides by alternative RNA splicing of an internal exon buried within the first intron of the gene. A chicken beta-crystallin cDNA (Beta35) has been partially sequenced and used to isolate its gene from a DNA library; at least 3 other Beta-crystallin genes (Beta19/26, Beta23 and Beta25) have also been obtained from this library. Developmental studies indicate that these Beta-crystallin genes are regulated independently during lens cell differentiation. The entire chicken Delta-crystallin gene locus and a complete duck Delta-crystallin gene have been cloned and mapped with restriction enzymes. There are two Delta-crystallin genes, tandemly arranged, 7-8 kilobases apart. The putative promotor flanking the 5 feet region of gene 1 has been identified and subcloned in pBR322. The complete sequence of the Delta-crystallin cDNA from gene 1 has been determined. A new crystallin (tau-crystallin) has been discovered and purified from the turtle lens. Experiments on the expression of cloned crystallin genes and hybrid genes in cultured lens cells have been initiated. Thus, the molecular genetics of the lens crystallins has been advanced to the point wehre functional studies on their expression may be performed.